Author: Kamil Yavuzer (Turkey)
Co-authors: Mehmet Citirik, Fatma Bağcı
Myopia is a growing major public health problem around the world. High myopia (HM) has conventionally been defined as a spherical equivalent refractive error exceeding -6.0 diopter (D) and/or an axial length longer than 26.5 mm. HM is the primary cause of uncorrected visual acuity loss and the main cause of low vision and blindness worldwide. Pathological myopia (PM) is different from other types of myopia in that it causes not only uncorrected visual acuity loss but also loss of best-corrected visual acuity. PM was firstly defined as the presence of structural changes that cause vision loss in the context of PM. However, although axial elongation is generally believed to play a key role in degenerative changes, axial elongation is not the only marker of PM. However, beyond the cut-off value in PM, the prevalence of PM increases exponentially. PM is commonly defined as myopia with posterior segment complications due to progressive and excessive elongation of the eyeball. The aim of this study is to investigate thickness alterations of each macular retinal layers in pathological myopic eyes and understand retinal perfusion by comparing the thickness of each retinal layer in eyes with PM and control group.
University of Health Sciences, Ankara Ulucanlar Eye Training and Research Hospital, Ankara/TURKEY
The patients were divided into the following two subgroups: The first group is the 'myopic group' with a spherical equivalent between -6.00 and -10.00 D and an axial length between 26.5 and 28.5 mm, the second group is the 'control group' with a spherical equivalent between -1.00 D and +1.00 D and axial length between 22.00 mm and 24.00 mm. In this study, the META-analysis for Pathologic Myopia Study Group classification was used and the cases included in the study and accepted as pathological myopia were with the unaffected macular area and additional degenerative chorioretinal findings. Moreover, the cases had additional chorioretinal degenerative findings except for the macular region. Fifty-one eyes of 34 patients in the myopia group and 51 eyes of 26 patients in the control group were included in the study. Total retinal thickness and each retinal layer thickness in the macular region was measured by using spectral domain optical coherence tomography (HRA2-Heidelberg Retina Angiography - Optical Coherence Tomography, Heidelberg Engineering, Germany) device. The densities of radial peripapillary capillary plexus (RPCP), superficial capillary plexus (SCP), and deep capillary plexus (DCP) were obtained by optical coherence tomography angiography (OCTA) instrument (RTVue XR Avanti, version 2017.1.0.151; Optovue, Inc., Fremont, USA).
There was no significant difference between the pathological myopic group and the control group in terms of age, gender, and intraocular pressure (p = 0.087, p = 1.000, and p = 0.960, respectively). However, compared with the control group, patients with PM had more refractive errors, worse best corrected visual acuity, and longer axial lengths (p <0.001, p <0.001, and p = 0.009, respectively). A summary of demographic data and comparative statistical analysis for the PM group and the control group are given in Table 1. The thicknesses of each retinal layer were measured with retinal segmentation analysis and the results are shown in Tables 2 and 3. Based on the OCTA images, RPCP density was found 46.89 ± 2.42% in the myopic group, 49.44 ± 2.83% in the control group, and there was no statistically significant difference between the groups (p= 0.381). SCP density was 41.18 ± 0.68%, DCP density was 42.90 ± 1.36% in the myopic group, while SCP density was 48.03 ± 1.33% and DCP density was 49.33 ± 2.51% in the control group. It was observed that the density was less in both SCP and DCP in the myopic group (p= 0.003 and p= 0.040, respectively).
This study shows that there is a thinning in total retinal thickness in PM. This thinning is predominantly in the outer retina in the fovea, whereas it is in both of the inner and the outer retinal layers in extrafoveal regions. Although there is thinning in the inner retinal layers, the absence of the decrease in retinal nerve fiber layer thickness can be interpreted as RPCP is less affected than other SVP and DVP areas in high myopia. We think that any evidence demonstrating a vascular insufficiency environment in certain sublayers of the retina in PM may be indicative of vascular diseases affecting retinal and choroidal circulation. In this connection, it may be illuminative for researchers to investigate each retinal layer separately in their future studies. Changes in retinal layer thicknesses and capillary plexus densities are observed in PM. Accordingly, evaluating the thickness of each retinal layer separately may be a marker in vascular diseases affecting the retinal and choroidal circulation.
The authors received no grants and funds in support of the study.